There is an increasing need for accurate position determination in, e.g., applications in the field of virtual/augmented reality and in connection with robot control. Today, various positioning systems based on ultrasound transmitted from identification tags are available for this purpose.
The low value of velocity of sound of 340 m/s means that a system based on ultrasound is limited with regard to how often an acoustic identification tag can transmit a signal and thus have its position updated. This problem is particularly noticeable if there are several identification tags that are to be positioned at the same time since, in addition to position, the identity of each individual identification tag must also be known.
Another problem is that known acoustic positioning systems are relatively sensitive to interference, e. g., the rattling of keys can often cause the system to fail.
The most common way of solving the said problems is to have a secondary channel in addition to a primary acoustic channel. The secondary channel is usually radio waves (RF), but may also be based on infrared light (IR). The extra channel is normally used to prompt one identification tag to transmit a signal. In that way, it is possible to know which identification tag has transmitted via RF/IR and obtain its position via the ultrasonic signal transmitted by the identification tag.
Systems based on a combination of ultrasound and RF/IR require both identification tags and detector units to contain more electronics, which means they will be more complex and consume more power. This may especially be a problem for the identification tags which it is often desirable to make as small as possible since they are to be attached to the different articles whose position is to be determined.
The object of the present invention is to be able to determine the position of several identification tags at the same time, without using more than one communication channel.